In domestic fuel cell systems, a start-up/stop operation in which a fuel cell repeatedly generates power and stops depending on electric power consumption of daily life is excellent in light of energy effective utilization, such as a reduction in charges for heat and electricity.
For the purpose of flexibly dealing with the start-up/stop operation, technical problems and their countermeasures regarding the repeated operation of the power generation and stop of the fuel cell are reported. Among these, one example of the techniques regarding the hydrogen generator is that in a fuel cell system, a hydrogen generator including a reformer generates and supplies a fuel gas, and supply of a material gas and steam stops during the operation stop. At this time, remaining steam condenses inside the reformer, and the reformer becomes a negative pressure state. This negative pressure state may cause problems, such as damages on the reformer and leakage of a combustible gas. Reported as means for resolving the negative pressure state is a technique of injecting a raw material gas to carry out pressure compensation (see PTL 1, for example).
Also reported as the means for resolving the negative pressure state is a technique of injecting steam to carry out the pressure compensation (see PTL 2, for example).